Re: [PATCH v1 bpf-next 1/8] selftest: bpf: Use BPF_SOCK_OPS_ALL_CB_FLAGS + 1 for bad_cb_test_rv.

[sashiko-bot@kernel.org]

Thank you for your contribution! Sashiko AI review found 1 potential issue(s) to consider:
- [Medium] Using `BPF_SOCK_OPS_ALL_CB_FLAGS + 1` to test invalid BPF callback flags creates brittle test logic that assumes contiguous bitmasks and breaks forward compatibility.
--

commit dfed6c2387074d0f6f7afb70b6bba777371f7267
Author: Kuniyuki Iwashima <kuniyu@google.com>

selftest: bpf: Use BPF_SOCK_OPS_ALL_CB_FLAGS + 1 for bad_cb_test_rv.

Once bpf_sock_ops_cb_flags_set() supports a new flag,
tcpbpf_user.c fails due to the hard-coded max value, 0x80.

> diff --git a/tools/testing/selftests/bpf/prog_tests/tcpbpf_user.c b/tools/testing/selftests/bpf/prog_tests/tcpbpf_user.c
> index 7e8fe1bad03f5..e4849d2a2956f 100644
> --- a/tools/testing/selftests/bpf/prog_tests/tcpbpf_user.c
> +++ b/tools/testing/selftests/bpf/prog_tests/tcpbpf_user.c
> @@ -26,7 +26,8 @@ static void verify_result(struct tcpbpf_globals *result)
>  	ASSERT_EQ(result->bytes_acked, 1002, "bytes_acked");
>  	ASSERT_EQ(result->data_segs_in, 1, "data_segs_in");
>  	ASSERT_EQ(result->data_segs_out, 1, "data_segs_out");
> -	ASSERT_EQ(result->bad_cb_test_rv, 0x80, "bad_cb_test_rv");
> +	ASSERT_EQ(result->bad_cb_test_rv, BPF_SOCK_OPS_ALL_CB_FLAGS + 1,
> +		  "bad_cb_test_rv");

Is BPF_SOCK_OPS_ALL_CB_FLAGS + 1 robust for forward compatibility?

When the test is compiled, BPF_SOCK_OPS_ALL_CB_FLAGS + 1 is evaluated to a
hardcoded value. If this compiled test runs on a future kernel where this value
is supported, the helper will successfully set the flag and return 0. The
userspace test would still expect the hardcoded remainder, causing it to fail.

Furthermore, this assumes contiguous bitmasks. If a flag is ever deprecated or
skipped, adding 1 could overlap with valid bits.

Would it be better to use a safely distant bit, such as 1 << 30, to guarantee
the flag remains unsupported and the test doesn't break in the future?

-- 
Sashiko AI review · https://sashiko.dev/#/patchset/20260508073355.3916746-1-kuniyu@google.com?part=1